A collimator is used, for example, when imaging with the aid of an X-ray machine, for example a computed tomography unit. Arranged on a rotary frame, the computed tomography unit has an X-ray system with an X-ray source and an X-ray detector. The X-ray detector is generally constructed from a multiplicity of detector modules that are lined up against one another in a row or in two dimensions. Each detector module of the X-ray detector includes, for example, a scintillator array and a photodiode array that are aligned with one another.
The mutually aligned elements of the scintillator array and of the photodiode array form the detector elements of the detector module. Arranged above each scintillator array in order to reduce influences of scattered radiation is a collimator which has the effect that only X-radiation of a specific spatial direction reaches the scintillator array. The X-radiation impinging on the scintillator array is converted into light that is converted into electrical signals by the photodiode array. The electrical signals form the starting point of the reconstruction of an image of an object being examined using the computed tomography unit.
The collimators of the detector modules of the X-ray detector have collimator plates that are aligned with the focus of the X-ray source of the X-ray machine, are fixed in plastic parts and are positioned relative to one another. The fixing of the juxtaposed collimator plates is performed on the top side and underside of the collimator. The detector modules with the collimators are arranged in a computed tomography unit on a so-called detector arc of the rotary frame. The detector arc is arranged opposite the X-ray source on the rotary frame, that is to say the rotating part of the gantry of the computed tomography unit.
The trend toward larger detector widths in the direction of a planar detector having a multiplicity of detector modules, as well as toward higher speeds of the rotating part of the gantry also leads to longer collimator plates. The problem arises here that as the detector arc rotates the collimators arranged at the ends of the detector arc are, in particular, acted upon by forces of such a nature that the collimator plates of these collimators are bent out of form as a consequence of the forces acting. This bending or deformation of the collimator plates can go so far that when an object is being examined these collimator plates cast an X-ray shadow and thus lead to image defects.